Mix sugar, strawberries, rhubarb, flour, lemon peel, and cinnamon together and place into a 9"x13" baking dish.

Mix butter, brown sugar, 1 cup flour, and rolled oats until crumbly, using a pastry cutter. Sprinkle over top of fruit. Bake at 375° for about 45 minutes or until fruit is soft and the top is lightly browned.